Liquid propellant rocket engines (LPREs) use a chemical reaction between one or more propellants under pressure to generate thrust to propel a vehicle. The chemical reaction occurs in a combustion chamber of a rocket engine nozzle, producing thrust as the reaction products are forcefully expelled from the engine. To produce suitable thrust from the rocket engine, the one or more propellants must be pressurized. Pressurization can be achieved by storing one or more propellant(s) at a specified pressure or by using mechanical pumps to drive the flow of the propellants into the combustion chamber. Mechanical pumps used to pressurize the propellants may be powered by turbines, which in turn are driven by the flow of vaporized propellants. Propellants may be vaporized by heating, and thus expanding, the one or more propellants in a nozzle wall as combustion occurs in the rocket engine nozzle. Alternatively, some turbines do not use the flow of propellants to generate power and may be powered by exhaust gas resulting from the combustion of small quantities of the propellants.
Each of these methods has associated disadvantages. For example, the process of vaporizing propellants using heat generated in the combustion chamber has limitations to the types of propellants used in addition to the thrust generated by the engine. In another example, a gas generator process has limitations because a portion of each propellant is combusted in the gas generator and discarded as exhaust. Thus, in a gas generator process, each propellant is not used in its entirety to generate thrust from the rocket engine nozzle.